In the "modern synthesis" of Darwinian natural selection and population genetics, evolution is driven by a dynamic involving genes and traits. A gene or array of genes codes for the production of a trait in the development of an organism. In turn, the trait contributes to the preservation of the genetic factors. This applies not only to physical traits such as mammary glands, but to behavioral traits as well. Why does this particular bitch invest time and precious resources nursing her litter? She does so because her mother did so and her grandmother and great grandmother, etc.
This theory is among the most robust in modern science. However, like all good science, it is subject to challenges. One of the theoretical problems that emerged early is the problem of altruism. Altruism is defined in biology as a behavior that involves a Darwinian sacrifice by on individual on behalf of another. A honey bee worker is capable of reproduction but sacrifices the opportunity to make use of that capacity in favor of service to the queen. The explanatory problem goes like this: if the theory of natural selection is correct, genes that code for altruistic behavior ought to put themselves out of business. An individual who is more reproductively selfish should be more reproductively successful. That should result in her genes proliferating in the population, leading to the eventual extinction of the altruistic genes.
For decades, evolutionary theorists employed the concept to inclusive fitness to solve the problem. When does an altruistic behavior promote the genes that code for it? It does so when it contributes to the replication of more copies of my own genes carried by my relatives.
This was expressed in a simple formula called Hamilton's rule: rb > c. Here r is relatedness. I am related to my brother by a factor of .5, meaning that we share about half our genes. I got the good ones. I am related to my aunt by a factor of .25, to my first cousin by a factor of .125, and to a second cousin by .312. The altruistic behavior may benefit one or more of my relatives, so b is that number. By definition, altruistic behavior involves a Darwinian cost, meaning that it reduces the probability that I myself will enjoy reproductive success. So c indicates that probability. A honey bee who gives up reproduction altogether pays a cost of 1.
So by this calculation, it makes very good Darwinian sense for me to risk or even sacrifice my life on behalf of three brothers: .5 x 3 > 1. I get more copies of my genes into the next generation if all three brothers bear children than I do if I bear children and they do not. Thus genes that code for familial sacrifice proliferate better than genes that code against it.
This has been regarded as a very robust theory. It explains why human beings are more likely to cooperate with near kin than with strangers and why a band of genuine brothers has proven to be such an effective fighting force throughout history. It also explains honey bees. These creatures are haplodiploid, meaning that females have two sets of genes (diploid) whereas males have only one set (haploid). One the queen mates with only one male, the honey bee sisters are more closely related to one another (.75) than to their own sons (.5). Since they cannot mate, they can have only sons. The result favors cooperation with their sisters for the good of the colony over trying to reproduce on their own. Many highly organized insect societies (bees, ants, and wasps) have this reproductive system; ergo: inclusive fitness explains the hymenoptera superorganisms.
Or so the theory has it. Recently this solid theory has been challenged by a scientist who was once one of its most powerful advocates. E. O. Wilson, the founder of sociobiology, has concluded that the theory is wrong. Most of the haplodiploid insects did not evolve into superorganisms. Termites did so, but they are not haplodiploid. Wilson thinks that Hamilton's rule is not very useful.
This challenge has created a lot of friction and heat. I won't go into the details here. The gist is that Wilson thinks that the close relatedness of honey bees, for example, is a result of a strong social organization rather than its cause. Altruism develops when a special set of adaptations virtually forces individual organisms to cooperate with and make sacrifices on behalf of their fellow organisms. Only once those conditions occur do a lot of brothers and sisters end up hanging around one another long enough for something like inclusive fitness to kick in.
I have been teaching inclusive fitness in my Biopolitics class for over ten years. I will continue to do so for the time being, as it is still the dominate theory. However, I not only suspect that Wilson is right, I hope he is right. The reason is that Wilson's current thinking points in the direction of group selection. This is the idea that natural selection can favor traits that benefit one group over another within a larger population, even if that trait involves a disadvantage for within group competition. This explains why ants and anthropoi have all but inherited the earth. For an excellent summary of this idea, see E.O. Wilson and D.S. Wilson (2007).
I think that this is one of the trends in modern biology that is bending the science back around toward Plato and Aristotle. So far I might be the only one who thinks that. So far.
As a postscript, let me say that I have no patience for anyone who tries to end an argument by appealing to "settled science."